“You’re gonna get fat”

Lately when I eat something like pizza or chocolate my boyfriend will say “you’re gonna get fat” in a jokingly way. I’m 4’11 and only weigh 92 pounds. I’m not perfectly happy with myself but I’m the ideal weight for my size.. It hurts my feelings when he says this and I’ve told him before. Why is he saying this to me when I’m not even a bit overweight?? Idk if he is truly just joking with me or if there’s something behind it.